So as to meet the demand in recent years for small, lightweight, high speed, highly functional electronics, IC chip-sized elements are connected when mounting a semiconductor, as in Chip Size Package (CSP) and the like.
In addition, tests of electrical properties, such as a burn-in test, are required to be done at die stages. For this end, a flexible film carrier has been developed to connect fine-pitched IC chips and to provide contact points for testing. The film carrier has connection points, i.e., bump contact points, at which point a test subject and a mounted element come into contact with each other on an insulating substrate (Japanese Patent Unexamined Publication No. 62-182672).
For forming bump contact points, an electroplating by an immersion method and a jet stream method has been conventionally applied. From the technical aspect, however, developments have been mostly made with respect to semiconductor wafers with the aim of eliminating abnormal precipitation of bump contact points and for forming bump contact points having a uniform height. For example, in Japanese Patent Unexamined Publication No. 2-61089, a liquid jet nozzle and the surface to be plated are kept parallel to each other for secondary fluctuation of the nozzle, so as to prevent deformed bump contact points produced due to the flow direction of the plating solution on the surface to be plated. According to the method utilizing a jet stream cup (Japanese Patent Unexamined Publication No. 4-315434), wafers are maintained by a control member and plated while floating horizontally on an overflowing plating solution, whereby bump contact points having a uniform height are obtained.
However, unification of the height of bump contact points is mostly studied with respect to plating using a plating solution without a brightener, namely, plating with precious metals (e.g., gold and silver) or solder (e.g., tin and zinc), without a brightener, and there appear to be very few studies of bump contact points which involve the use of a gloss plating solution containing a leveler and a brightener, and a jet stream type plating apparatus, so as to examine abnormal bump contact points associated with deformation and absence of formation.
For example, as disclosed in Japanese Patent Unexamined Publication No. 7-11498, the area of an insoluble anode is set to not less than 0.5 times the plating area and not more than 5 times that, so as to prevent or suppress decomposition of the brightener in an insoluble anode. The insoluble anode means anodes which are not dissolved in a plating solution, and which generally comprise a metallic core of titanium, niobium and the like and a coating of platinum on the surface of the core. Some of them have a surface covered by iridium.
The brightener for copper sulfate plating includes, for example, high molecular weight leveler (e.g., polyethylene glycol) and a brightener (e.g., bis(3-sulfopropyl)disulfide). A brightener is significantly decomposed in a jet stream type plating that catches much air, which in turn often causes imbalance of the components of the brightener.
When copper bump contact points are formed using an imbalanced plating solution, the bump contact points tend to be flat as compared to normal mushroom-shaped bump contact points, and are easily affected by the liquid flow, thus resulting in the vertex of the bump contact point being slipped in the flow direction and greater variations in height. Further imbalance results in no gloss but rough surface of the bump contact point. If gold is plated on a copper core formed using a plating solution containing an imbalanced brightener, contact failure in electrical testing and defective connection to IC chip in mounting a semiconductor mounted are observed.
When compared to a plating solution showing good throwing power, such as that to be used for gold plating and the like, a plating solution containing a brightener easily catches air bubbles, which tendency becoming prominent when using a jet stream plating apparatus wherein the object to be plated is faced downward and a liquid is spouted out from underside. These air bubbles prevent growth of bump contact points and cause less height or deformation thereof, even if bump contact points can grow at all, which in turn leads to contact failure in electrical testing and defective connection to IC chip in mounting a semiconductor, as mentioned above.
It is therefore an object of the present invention to solve the above-mentioned problems and provide a production method of a circuit substrate having bump contact points free of abnormal precipitation and nonuniform height, and a jet stream type plating apparatus to be used therein.